Welding-related parkinsonism: Clinical features, treatment, and pathophysiology

To the Editor:

We read with interest the case-control study in which Racette et al. compared the clinical features of welding-related parkinsonism and idiopathic PD.1 They found that age at onset was much younger in welders and reached the conclusion that welding may be a risk factor for PD, possibly due to prolonged manganese exposure.1 In the same issue of Neurology, this finding is discussed in an editorial.2 Whereas the general principle that environmental factors may play a role in PD is accepted, the author points out that no exogenous agent has been consistently linked to PD. Welders are a relatively small group not comprising the whole of the PD patient population. Alternative strategies should be adopted to identify the environmental causes of PD—a task that is “akin to looking for needle in a haystack” in view of the large number of candidates.

Last year, Neurology published our larger case-control study of 990 patients with PD, in which the clinical features of patients with a history of exposure to hydrocarbons were compared to those of patients without such history.3 The age at onset was younger in our study and led us to the same conclusion as that of Racette et al.; namely, that an environmental factor accelerates the onset of PD.

We also found that the disease was more severe throughout its course. This finding was not reported by Racette et al.1 However, they compared the Hoehn & Yahr class as an index of severity, which is notoriously less sensitive than the methods we used—the Unified Parkinson’s Disease Rating Scale (UPDRS) and the apomorphine test.

Hydrocarbons are commonly found in the environment, as they are constituents of varnish, glue, and many petroleum derivatives. Twenty percent of our patients had a history of exposure to …